Fuel efficiency and performance of an internal combustion engine may be improved by varying the timing of intake and/or exhaust valves. One way to adjust valve timing is to use a variable event valvetrain that is capable of adjusting valve timing either dependant on or independent of engine position.
One method to control a variable event valvetrain during an engine start is described in U.S. Pat. No. 5,765,514. This method provides for closing the intake and exhausts valves after the ignition switch is turned on, provides a predetermined delay, and then uses the starter to crank the engine. The cylinders are set to the exhaust stroke, suction stroke, compression stroke, and explosion stroke, respectively as the position of the engine is determined.
The above-mentioned method can also have several disadvantages. Namely, it appears that the method powers up the valvetrain and starts the engine when power is supplied to the engine control system. In other words, when the operator uses a key to signify that he wishes to operate the engine the control unit receives power and engine is cranked. However, if the driver merely wishes to use the key switch to power engine accessories, for example, it is indeterminate what the state the valvetrain will assume. Further, if the vehicle has a key switch and the operator toggles an ignition key between the “engine stop” and “engine accessory” position a number of times then it is also indeterminate how the valvetrain will be operated.
The inventor herein has recognized the above-mentioned disadvantages and has developed a method to control engine valves during stopping and starting that offers substantial improvements over previous methods.